This invention relates in general to structural frames and in particular to a new and improved metal door frame construction for use in the assembly of large doors for industrial or agricultural buildings.
While the present invention is useful in the fabrication and assembly of frames for many purposes, the disclosure will be facilitated by addressing the specific problem of providing reliable and inexpensive door frames for relatively large sliding doors, of the type utilized with industrial or agricultural buildings such as barns, or the like. In such structures, on-site construction and assembly of the doors is generally desirable due to the advantages in shipping the doors in "knock down" form, rather than in the fully assembled mode. Once the door frame is assembled, corrugated metal siding or panels are attached to the frame.
The manufacturers of such doors and door hardware have recognized the existence of a number of problems as to weight, difficulty of assembly and reliability in service of such door frames. Initially, it will be appreciated that weight as well as overall size presents a problem to the assembler and installer, as such doors are generally in the range of eight feet-by-eight feet, or larger. Accordingly, there has been developed a need for a door frame that can be easily fabricated by the installer at the jobsight, with a minimum amount of handling, and without the use of a great number of separate fastener elements to maintain the frame elements in assembly. An example of one approach to this problem is found in U.S. Pat. No. 4,021,988, wherein upright channels and cross channels are interfitted to form a frame, and locked together by means of pre-punched tongues which are bent or deformed inwardly to interlock with slots, to maintain the channel member in assembly. This particular type of joint or attachment means is intended to hold the end edges of the cross channel member in firm flush engagement with the web portion of the upright channels, thus insuring squaring of the assembled door frame components. Recognizing, however, the relatively light gauge metal utilized in this type of structure, the tongues may weaken or even break off in service, or while the door frame is being handled during installation. More specifically, the described prior art structure requires the inward bending of tongues on both sides of the upright channels to complete the assembly of the frame. Accordingly, the workmen must initially lay out the channel pieces and bend the tongues on one side and then flip over the entire, partially assembled, frame in order to bend in the tongues at the opposite side. As the structure is relatively large and heavy, this procedure places a considerable burden on the installer. But more to the point, this "flipping over" places considerable forces upon the partially assembled frame, which may cause the tongues initially bent over to loosen and the frame to go out of square before the assembly of the siding can be completed. These problems are particularly severe with door frames of the large size generally utilized for barn doors. Moreover, it will be appreciated, that in service or during movement to complete assembly, considerable moment is exerted by the long cross channels as compared to the relatively small opposing force exerted by the bent over tongue members. The resulting moment tends to pull the assembled door out of square. It will be appreciated that once these tongues are loosened, even slightly, the forces opposing relative pivotal movement of the cross pieces are greatly diminished.
Accordingly, it is a general object of this invention to provide a new and improved metal door frame construction which overcomes many of the problems encountered in prior art structures. A more specific object is to provide a metal door frame construction which is adapted both to lock the respective channel members in engagement and to prevent relative pivotal movement therebetween, so as to hold the assembled frame structure substantially in squared relation. Another object is to provide a metal door frame construction, in accordance with the foregoing objects which may be relatively easily assembled by a single workman, without requiring any flipping over or lifting of the structure until assembly is complete. Briefly, the foregoing objects, and others are achieved by a metal door frame construction according to the present invention which provides a novel joint for the interconnecting of the cross channels to the upright channel. In this regard, detent means are utilized to maintain initial assembly and prevent lateral displacement. Further, detent means are employed to prevent relative pivotal movement between the channel members. The respective detent means are, as will be explained more fully hereinafter, designed to provide a snap-fit type of joint, that can be easily achieved without special tools or the necessity of having to turn over the frame before attaching the siding.
Other objects, features and advantages of the invention will be more readily appreciated upon consideration of the following detailed description, together with the accompanying drawings.